This invention relates to high temperature thermal (heat transfer) fluids, and more particularly to heat transfer fluids comprising blends of 1,2,3,4 tetrahydro(1-phenyl-ethyl)naphthalene and an alkyl biphenyl.
Heat transfer fluids (also denoted as xe2x80x9cthermal fluidsxe2x80x9d) are widely used for temperature control in manufacturing facilities. The ability of a heat transfer fluid to resist degradation at elevated temperatures is referenced through a performance property denoted as xe2x80x9cthermal stabilityxe2x80x9d. As a heat transfer fluid undergoes degradation, both volatile materials (which xe2x80x9cboilxe2x80x9d or evaporate from the fluid) and xe2x80x9cheavyxe2x80x9d materials (also denoted as xe2x80x9chighersxe2x80x9d or xe2x80x9cresiduexe2x80x9d) are formed within the heat transfer fluid. Such heavy components elevate the heat transfer fluid""s viscosity and thereby lead to an increase in film temperature in the portion of heat transfer fluid denoted as the xe2x80x9cfilmxe2x80x9d which exists at the interface of the heat transfer fluid and a high temperature (respective to the temperature of the fluid) surface; any such differential in film temperature above the temperature of the less viscous portion of the heat transfer fluid augments the rate of degradation in the heat transfer fluid as a whole insofar as the film portion intermixes with the remainder of the heat transfer fluid. Further, polymers formed through the degradation of a heat transfer fluid tend to darken the fluid and ultimately deposit on surfaces in the system; these deposits are detrimental to system efficiency and potentially lead to system failure. Significantly, degraded heat transfer fluid must, therefore, be periodically replaced with fresh or recycled heat transfer fluid.
The long-standing importance of finding heat transfer fluids exhibiting improved thermal stability is evidenced, for example, by Matsumoto et al., Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, no. 3, 1976, pp. 215-218, which is herein incorporated by reference. Matsumoto tested the thermal stability of 1-phenyl-1-tetrahydronaphthyl-ethane (PTE, also called 1,2,3,4-tetrahydro(1-phenylethyl)naphthalene which is abbreviated herein as ST-THN) and compared the results with thermal fluids such as dibenzyl benzenes and partially hydrogenated terphenyls which are well-established heat transfer fluids in the industry. Matsumoto""s results showed ST-THN to have favorable properties for a high boiling point thermal fluid. Matsumoto also identified the degradation products from ST-THN. Although ST-THN was found to have favorable properties alone, its compatibility with other heat transfer fluids was not investigated.
In industrial applications, the ability to mix different thermal fluids without the detrimental effects described above is advantageous. Therefore, a cost-effective heat transfer fluid blend having favorable thermal stability properties is desirable.
This invention is a heat transfer fluid which comprises a mixture of 1,2,3,4-tetrahydro(1-phenylethyl)naphthalene (ST-THN) as a first fluid component and an alkyl biphenyl as the second fluid component. It has been discovered, surprisingly, that mixing ST-THN with specific second fluid components as described herein yields a heat transfer fluid with a thermal stability property significantly improved over the thermal stability of either of the components prior to their blending.
The heat transfer fluid is beneficially admixed from 1,2,3,4-tetrahydro(1-phenylethyl)naphthalene; and a second fluid characterized as an aromatic component having alkyl, cyclohexyl, or cyclopentyl linkages; preferably, alkyl linkages. The second fluid is preferably other than a degradation product of 1,2,3,4-tetrahydro (1-phenylethyl)naphthalene.
More specifically, the heat transfer fluid is admixed from: 1,2,3,4-tetrahydro(1-phenylethyl)naphthalene; and a second fluid selected from the group consisting of dibenzyl toluene, partially hydrogenated terphenyl, dibenzyl benzene, xylyl toluene, dixylyl toluene, xylyl xylene, dixylyl xylene, diethylbenzene, 1,1-diphenylethane, benzene alkylates, alkylnaphthalenes, alkyl biphenyls, diphenylmethane, cyclohexyl-diphenyl ether, alkyldiphenylethers, triphenylmethane, tritolylmethane, and mixtures thereof.
More specifically, the heat transfer fluid is admixed from: 1,2,3,4-tetrahydro(1-phenylethyl)naphthalene as a first fluid component and a second fluid component selected from the group consisting of a partially hydrogenated terphenyl, an alkyl biphenyl, and mixtures thereof; the alkyl biphenyl is selected from the group consisting of 1,1-diphenylethane, methylbiphenyl, ethylbiphenyl, diethylbiphenyl, triethyl-biphenyl, propylbiphenyl, dipropylbiphenyl, isopropylbiphenyl, diisopropylbiphenyl, butylbiphenyl, dibutylbiphenyl, and mixtures thereof.
Another embodiment of the present invention is a method for preparing a heat transfer fluid. The method comprises admixing a first fluid component of 1,2,3,4-tetrahydro(1-phenylethyl)naphthalene with a second fluid component as described above. The 1,2,3,4-tetrahydro(1-phenylethyl)naphthalene component preferably constitutes at least 10 percent by weight of the total heat transfer fluid.
A further embodiment of the present invention is a method of controlling the temperature of a system. The method comprises adding to the system a first fluid component of 1,2,3,4-tetrahydro(1-phenylethyl)naphthalene and a second fluid component as described above. The 1,2,3,4-tetrahydro(1-phenylethyl)naphthalene and the second fluid component are, in one embodiment, added to the system separately, or, in another embodiment, admixed together prior to addition to the system.